The invention relates to improvements in methods and mechanism for forming bags with interlocking continuous fasteners or zippers thereon wherein the bags are formed of a thin plastic film, and delivered with the profiles in separated condition. The continuous material is normally formed by an extrusion process with the profiles automatically interlocked during the completion of the process, as exemplified in the teachings of U.S. Pat. No. 3,340,116, Naito.
In making bags from material of this type, the film, which is very thin on the order of several mils is formed with the fasteners normally being integral thereon. The profiles are interlocked so that they will maintain their shape during the time the film is stored on a roll and handled and shipped. Individual bags are made from the continuous roll of film by cross-cutting ends off of the layers of film and sealing the edges. The individual bags are then used by pulling the interlocked rib and groove fasteners apart by flanges provided above the profiles so that the bags can be filled and resealed.
It has been generally customary to produce such bags with a closed top and the profiles engaged, and the user must, therefore, separate the top edges of the bag by separating the rib and groove elements when the bag is to be filled. The bags have come off of the bag machine with interlocked profiles, and separation must be made before the bags can be used and filled. This is an extra operation which consumes effort and time. Where the bags are to be hand loaded, it normally requires about 50% more time than if the bag were available with an open top with the profiles separated. Where automatic loading is used, a method has to be provided to open the profile in order that the bag can be delivered to the filling station with the top open. Efforts have been made to separate the rib and groove elements at different positions before cross-sealing and cutting the bags, but these have been proven unsuccessful in that when the rib and grooves are separated and cross-sealing takes place, the rib and groove often do not rejoin. Either they stay apart of miss each other so that the rib is beside the groove. If this occurs, the bag cannot thereafter be effectively sealed because when the rib and groove are attempted to be pressed together, the rib does not start into the groove, but presses beside it so that the fastener never can interlock. This has particularly become the case with improved methods of manufacture and improved plastics which make it possible to make the rib and grooves very small and yet sufficiently strong to provide a good closing interlock. The smaller the rib and groove units, the more difficult it is to join them when the seal is formed at the edge of the bag, and as above stated, they must be joined at the edge or they will not interlock when a pressure is applied to attempt to interlock them and close the bag.
It is accordingly an important object of the invention to provide a method and structure for completing reclosable bags which have continuous interlocking elements along the top, and wherein the bag is opened, and the interlocking elements are separated after the bag is delivered to the customer. The same problem occurs and is solved by the invention where the customer makes the bags on his premises and desires to have an open bag to fill which does not have to be opened by a separate operation.
A feature of the invention is to take the continuous supply of bag material having opposing thin plastic film layers with interlocked facing rib and groove profiles along one edge and to insert a separating finger between the rib and groove profiles to separate them. They are separated, but the rib and groove profiles are maintained in opposing alignment with each other by traveling along in grooves in the separating finger with the grooves being sufficiently deep so that they guide the sides of the rib and groove, but do not engage the surfaces facing each other to in anyway flatten the rib and groove. A further feature of the invention then resides in immediately interlocking and cross-sealing the profile very close to the separating finger end while the profiles are maintained in exact alignment, and the profiles are brought into almost closed position just before joining and sealing so that the rib and groove elements move a minimum distance to engage and interlock when struck by the sealer.
Other objects, advantages and features, as well as equivalent methods and structures which are intended to be covered herein, will become more apparent with the teaching of the principles of the invention in connection with the disclosure of the preferred embodiments in the specification, claims and drawings, in which: